1. Field of the Invention
The present invention pertains to very wideband spiral antennas and, more particularly, to backlobe elimination in such spiral antennas in small, confined spaces.
2. Description of the Related Art
This section of this document introduces various aspects of the art that may be related to various aspects of the present invention described and/or claimed below. It provides background information to facilitate a better understanding of the various aspects of the present invention. As the section's title implies, this is a discussion of “related” art. That such art is related in no way implies that it is also “prior” art. The related art may or may not be prior art. The discussion in this section of this document is to be read in this light, and not as admissions of prior art.
One particular type of antenna is known as a planar “spiral antenna”. Spiral antennas take their name from the spiral shape of their radiating/receiving elements. As with most antennas, the planar spiral antenna radiates or receives from all directions, but primarily from the front side and the back side, more commonly known at the “frontlobe” and the “backlobe”. The backlobe is commonly undesirable, and the art has proposed a number of techniques for eliminating, or at least mitigating, such backlobes.
The classic technique absorbs the backlobe in a deep cavity (e.g., a depth that is twice the width of the antenna; for example, 3″) filled with a honeycombed dielectric material. Another approach is disclosed in U.S. Pat. No. 6,407,721, which we have not seen reproduced in the laboratory. However, all of the techniques proposed by the art have drawbacks associated with their benefits. The art therefore continues to seek alternative backlobe elimination techniques in reduced volume space and by simple designs allowing low cost embodiments.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.